Fig. 5. Response to large obstacles by C. bronzie. As found for T. cystophora (see Fig. 3), there are major differences between the response to the colored obstacles and the response to the transparent obstacles showing that the obstacle avoidance response is visually guided (A–C). There are also indications that the strength of the response follows the intensity contrast between the obstacle and the chamber wall (A–C; see Fig. 1D). The medusae performed more avoidances (A) and had less contact (B) when presented with the high contrast black obstacles (for statistics see Results). There was no significant difference between the responses to the two types of transparent obstacle (P>0.65). N=10 for A and B, but since not all medusae displayed avoidances, N values vary in C (shown as numbers in bars). Values are means and error bars indicate s.e.m. Trans, transparent obstacle; Trans+B, transparent obstacle with black top above water.